Sorry for the long delay, just arrived back from vacation.
The usual way to assign different materials according to slot blend modes is via a BlendModeMaterialsAsset, which can be assigned as a SkeletonDataModifier asset. See this documentation section: spine-unity Runtime Documentation: SkeletonData Modifier Assets
So you should be able to create a copy of the provided Default BlendModeMaterials
asset and name it e.g. TintBlack BlendModeMaterials
, assign the desired materials with your custom tint black shaders and assign the TintBlack BlendModeMaterials
asset at the _SkeletonData
asset's Skeleton Data Modifiers
.